That assurance came Sunday morning, and most of Endeavour's countdown proceeded without incident under clear skies.

By about 5 p.m., the crew had strapped into their seats.

But approaching storms soon became a concern. They ultimately violated two launch criteria, pushing within 20 miles of the shuttle landing site - a problem in the event of an early launch abort - and within 10 miles of the launch pad.

Endeavour's crew members plan to deliver and install the third and final piece of Japan's Kibo science complex at the station. They'll conduct five spacewalks.

Tuesday might be Endeavour's last chance to launch before July 27 because of an unmanned Russian cargo ship heading to the station later this month. Negotiations with the Russian Federal Space Agency could make Wednesday an option.